Protective helmets are widely used during athletic, industrial, and military activities (including, e.g., sports, motorcycling, construction work, and combat) to provide protection to the wearer's head in case of an impact or collision. For example, football and baseball players routinely wear helmets to reduce the effect of impact forces and diminish the risk of concussions or other head injuries. Protective helmets often include a rigid or semi-rigid exterior shell, e.g., made of a hard plastic material, for distributing impact forces over a wider area, and an interior liner for contact with the wearer's head. Located between the liner and the shell, or integrated with either, is usually a crushable, impact-absorbing layer (such as, e.g., a layer of foam or an arrangement of shock-absorbing fluid-dynamic cells) designed to eliminate or reduce the force of the impact on the wearer's head.
In many helmet designs, the liner, shock-absorbing layer, and/or shell are glued together or otherwise permanently adhesively affixed to each other across large surface portions, e.g., with a layer of VELCRO hook-and-loop fastener (or similar mechanical adhesive). Alternatively, in some helmets, the liner is screwed to the shell at the periphery. These conventional approaches to securing helmet liners are, generally, inconveniently practiced. The attachment of the liner with screws is tool-based, and the use of VELCRO can make correct placement of the liner into the shell difficult and corrections inconvenient. In addition, the hardware or adhesive layer required to attach the shell to the liner adds material and manufacturing cost to the helmet. Accordingly, secure and low-cost alternative helmet-liner attachment means would be desirable.